This invention relates generally to a furnace construction adapted for heating ceramic materials to significantly elevated temperatures wherein these materials are either sintered or otherwise reacted to form a wide variety of final products, such as phosphors, wear parts and the like. At elevated temperatures of 1000.degree. C. and above which are typically encountered in such type furnaces, the furnace construction itself is susceptible to both thermal shock and chemical attack occasioned by significant volatilization of the ceramic materials being processed. Such problems are especially aggravated in those furnaces requiring that the ceramic materials be moved during processing which can further cause serious physical abrasion to the ceramic materials and furnace parts being moved. Abraded material often combines with by products of the chemical reaction to form accummulations in the heated enclosure of the furnace, thereafter obstructing further movement of the ceramic materials through said heated enclosure.
The extent and seriousness of this general problem can be illustrated in the preparation of inorganic phosphors at temperatures often exceeding 1150.degree. C. in tunnel-type furnaces. Containers such as quartz trays or crucibles are filled with the phosphor powder and placed on plate-like ceramic tray members which now include opposing runner surfaces extending from one major surface of the individual tray members. The loaded trays are then transported by conveyor means to the furnace heated enclosure and pushed across a ceramic hearth member of the heated enclosure during the firing operation. While the known ceramic tray material itself, generally cordierite, exhibits satisfactory resistance to thermal shock and chemical attack when subjected to these elevated temperatures, the presence of a phosphor material produces a far different result. Specifically, phosphor volatilization products such as antimony and water vapor combine with the abraded material formed when the tray runners move across the furnace hearth surface to produce a glassy accummulation obstructing further passage of the loaded trays through the furnace. The furnace is thereafter required to be shut down to remove the obstructing accummulation or replace furnace parts in order to again permit tray movement through the furnace.
It would be desirable, therefore, to modify such furnace contructions so as to better resist the effects of physical abrasion occuring therein. It would further be desirable to do so with relatively modest structural changes in the furnace construction and which do not significantly alter the manufacturing operations.